There is conventionally a heat pump apparatus in which a compressor that compresses refrigerant, a condenser, an expansion mechanism, and an evaporator are sequentially connected to perform a refrigeration cycle, and, in the condenser or the evaporator, the heating energy or cooling energy of the refrigerant is transferred (heat-transferred) to heat medium.
The compressor includes a compression mechanism and an electric motor that rotatively drives the compression mechanism. The compression mechanism and the electric motor are housed in a sealed container. The high-pressure and high-temperature refrigerant compressed by the compression mechanism is once discharged into the sealed container. Thus, the electric motor is exposed to such high-pressure and high-temperature refrigerant. To smoothly rotate the compression mechanism, a machine oil (hereafter referred to as “refrigerating machine oil”) is stored in the sealed container.
The electric motor includes a stator fixed to the sealed container and a rotor that is surrounded by the stator and rotates. The rotor is coupled to the compression mechanism. The stator has a cylindrical shape and includes a back yoke part forming an outer periphery of the stator, plural teeth parts protruding from the back yoke part toward the center, and a winding wire (electric wire) wound around the teeth parts through intermediation of an insulating material (insulator).
In addition, as the insulating material (insulator), there is disclosed an invention using polyphenylene sulfide (PPS), which does not have ester bonds (for example, refer to Patent Literature 1).
Further, as the insulating material (insulator), there is disclosed an invention using polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), which have ester bonds (for example, refer to Patent Literature 2).
Regarding the refrigerant used for the heat pump apparatus, to prevent destruction of the ozone layer, chlorine-free refrigerants have come to be used as substitutes in recent years. However, there is a problem in that, such chlorine-free HFC refrigerants have a relatively high Global warming potential (GWP). Accordingly, measures to prevent the refrigerants from leaking outside the cycles have come to be taken, and recovery of the refrigerants at the time of disposal of the devices has become compulsory. However, a recovery ratio is not sufficient. Thus, use of a refrigerant that has an even lower GWP as a substitute is being considered.
As the refrigerant for stationary air-conditioning apparatus, R410A has been used. However, use of R32 refrigerant and other refrigerants having lower GWPs as substitutes is being considered.
In the EU, there is a movement toward mandatory use of refrigerants having even lower GWPs. The candidate refrigerants include natural refrigerants such as CO2 and, for example, a hydro-olefin-based refrigerant that is HFO-1234yf, or a propylene-based fluorohydrocarbon.
However, hydro-olefin has a molecular structure having a carbon double bond. In general, such functional groups having a carbon (double bond) or triple bond, in other words, (unsaturated hydrocarbons) such as alkenes and alkynes, have a feature of undergoing addition reactions with various molecules. Thus, compared with conventional refrigerants not having double bonds, the double bonds of the hydrocarbons tend to cleave, that is, the functional groups tend to react with other substances and the chemical stability is very poor.
For this reason, the following method has been disclosed: the surface of a slidable section that has high temperature in a compressor and on which decomposition or polymerization of propylene-based fluorohydrocarbon, which is one of hydro-olefins, tends to occur, is constituted by a non-metal part, to thereby suppress decomposition or polymerization of the refrigerant (for example, refer to Patent Literature 3).
Tetrafluoroethylene is useful as a monomer for producing fluororesins and fluorine-containing elastomers having excellent properties in terms of, for example, heat resistance and chemical resistance. However, tetrafluoroethylene has a very high probability of polymerization. Accordingly, to suppress the polymerization, a polymerization inhibitor needs to be added at the time of generation of tetrafluoroethylene. This technique has been disclosed (for example, refer to Patent Literature 4).